IFrame Problem

Hello friends,

in web page www.adwords.com there is IFrame.
i want to get controls/elements of this IFrame.
How can i do that. This is my VC++ code:

i written code::::

here g_lpHTMLDocument2 is IHTMLDocument2 pointer .
It contains valid document pointer.

IHTMLFramesCollection2Ptr pFrameColl;
hr = g_lpHTMLDocument2->get_frames(&pFrameColl);
if(SUCCEEDED(hr))
{
IDispatch *pDisp = NULL;
long lFrames = 0;
pFrameColl->get_length(&lFrames);
for ( long i = 0; i < lFrames ; i++ )
{
VARIANT varIndex, varDispatch;
VariantInit(&varIndex);
VariantInit(&varDispatch);
varIndex.vt = VT_I4;
varIndex.lVal = i;
if(SUCCEEDED(pFrameColl->item(&varIndex, &varDispatch)))
{
if(varDispatch.vt == VT_DISPATCH)
{
CComPtr pHTMLWnd2;
if(SUCCEEDED(hr = varDispatch.pdispVal->QueryInterface(IID_IHTMLWindow2,(LPVOID*)&pHTMLWnd2)))
{
IHTMLDocument2Ptr pHTMLDoc2;
hr = pHTMLWnd2->get_document(&pHTMLDoc2);
//HERE I M GETTING NULL PONTER ,ERROR IS ACCESS DENIED

IHTMLElementCollection* pElementColl = NULL;
pHTMLDoc2->get_all(&pElementColl);

}

pHTMLDoc2 DOES NOT CONTAIN VALID ADDRESS.

Can someone help

Harry